The present invention relates to a slant plate type hydraulic device comprising: a cylinder block; a slant plate arranged to face the cylinder block and to rotate relative to the same; a multiplicity of plungers arranged in a manner to freely slide in the axial direction of the cylinder block positioned in an annular array around the axis; and a shoe attached to the leading end of each of the plungers and held in sliding contact with the slant plate. More particularly, the present invention relates to either a slant plate type hydraulic pump which is adapted to increase oil pressure by turning the cylinder block and the slant plate relative to each other or a slant plate type hydraulic motor which is adapted to turn the cylinder block and the slant plate relative to each other by reciprocating the plungers.
In order to lubricate the sliding contact portions between the slant plate and the shoe of a slant plate type hydraulic device, it is known in the prior art to fill up the casing which accommodates the cylinder block and the slant plate with lubricating oil (as in Japanese Patent Publication No. 43-24627).
A hydraulic device having its casing filled up with lubricating oil, as has been described above, can sufficiently lubricate the sliding contact portions between the slant plate and the shoe but has a defect in that the resistance of the lubricating oil to movement or stirring by the rotating members, especially by the rotations of the plungers, is so high as to cause a reduction in the operation efficiency. If, with that defect in mind, the amount of the lubricating oil in the casing is reduced so as to lower the resistance to movement by the rotating members, the slant plate and the cylinder block are partially exposed above the surface of the oil to invite a fear of disadvantage that the slant plate and the shoe seize or wear because of shortage of supply of the lubricating oil.